Emulsion aggregation toners are excellent toners to use in forming print and/or xerographic images in that the toners may be made to have uniform sizes and in that the toners are environmentally friendly. U.S. patents describing emulsion aggregation toners include, for example, U.S. Pat. Nos. 5,370,963, 5,418,108, 5,290,654, 5,278,020, 5,308,734, 5,344,738, 5,403,693, 5,364,729, 5,346,797, 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,650,255, 5,650,256, 5,501,935, 5,723,253, 5,744,520, 5,763,133, 5,766,818, 5,747,215, 5,827,633, 5,853,944, 5,804,349, 5,840,462, and 5,869,215, all of which are incorporated herein by reference in their entirety.
Two main types of emulsion aggregation toners are known. First is an emulsion aggregation process that forms acrylate based, e.g., styrene acrylate, toner particles. See, for example, U.S. Pat. No. 6,120,967, incorporated herein by reference in its entirety, as one example of such a process. Second is an emulsion aggregation process that forms polyester, e.g., sodio sulfonated polyester toner particles. See, for example, U.S. Pat. No. 5,916,725, incorporated herein by reference in its entirety, as one example of such a process.
Fluorescent toners may be used as an authenticating feature in the document security industry. Secure documents, for example, documents that are difficult to forge, may be created using toners that include fluorescent agents either alone or in combination with ordinary pigments. Features printed using fluorescent toners are usually invisible under visible light, due to the colorless nature of the security inks or due to masking by other colorants in the document. Under ultraviolet illumination, however, the fluorescent features of the document are revealed in the form of a bright emission by the fluorescent dyes in the visible spectrum. For example, certain bank notes utilize visible features, such as holographic patches, microprinting and microtextures to conceal additional fluorescent threads and/or multi-colored emblems embedded in the bank note, which are only revealed under specific light frequencies. These features provide an increased level of security against counterfeiters by making the copying process of such a document more difficult. A fluorescent toner composition may also be used for digital imaging in tissues or other applications of interest as the fluorescence is easily detectable in the material that is to be imaged.
However, pigments are difficult to disperse into polymeric materials and gels on account of their lack of solubility, size, tendency to aggregate and physical property differences. A great deal of effort and time is spent dispersing pigments into aqueous dispersions using surface active agents (surfactants) which are detrimental to the performance of the parent particle in the final xerographic application. Ideally, the colorant used in emulsion aggregation should eliminate the need for this costly dispersion and eliminate the use of surfactants. Often dyes are used instead of pigments to overcome these shortfalls. However, dyes are expensive and so add cost to the final product. Dyes can furthermore affect the material's properties based on their loading and because of their low molecular weight lead to depressions of Tg and other such property modifications. These negative attributes all relate to the low molecular weight of the molecules in comparison to the gel or macromolecular matrix that holds them. In toners, this effect leads to a depression of the toner Tg along with the above-cited additional challenges. Ideally, the colorant used should therefore be derived from pigments, be compatible with the resin matrix and offer the above advantage of not necessitating dispersion processing. Finally, aggregation of the pigment in the final application can be another shortfall that leads to product (toner) failure. For highly pigmented toners this is particularly troublesome as it leads to high dielectric loss and therefore poor transfer of the toner to the page from the transfer belt. Ideally, this new colorant would also therefore be highly compatible with the resin such that it would not phase separate and produce a toner particle with a low dielectric loss.
Improved toners and methods for producing toners, which eliminates the need for pigment dispersions and high levels of surfactant, remain desirable. Such toners and processes may reduce production costs and effectively produce a particle with a homogenously distributed colorant.